The present invention relates to a technique for controlling a touch-detection position on a touch panel with respect to a display-scan position on a display device, and particularly to a technique in connection with a touch panel controller and a semiconductor device with a touch panel controller arranged in an on-chip form, and useful in application to e.g. an information terminal device having a touch panel integrated with a display device.
A portable information terminal device such as a tablet or a smart phone has, on its front face, a touch panel integrated with a liquid crystal panel, and is arranged to be able to determine what operation has been ordered from a touch coordinate where a multipoint touch has been performed on the touch panel according to screen display on the display panel. A mutual capacitance type touch panel which supports such multipoint touch has drive electrodes and detection electrodes arranged to intersect one another, and a number of detection capacitances formed at intersections of the drive and detection electrodes like a matrix. Such a touch panel integrates changes in voltage arising on the detection electrodes through the detection capacitances while driving the drive electrodes sequentially, thereby forming detection signals. In case that a finger is brought close to the detection capacitances, the stray capacitance of the finger is combined with the detection capacitances, and thus the combined capacitance values become smaller. A mutual capacitance type touch panel is arranged to discriminate between the states of “being touched” and “being untouched” based on the differences of the detection signals according to the changes of the capacitance values.
A liquid crystal panel has a thin-film transistor, which is referred to as TFT, arranged at each intersection point of the display-scan electrodes and signal electrodes arranged to intersect with one another. The thin-film transistors each have a gate connected to the display-scan electrode, and a source connected to the signal electrode, and a drain connected to a common electrode through a liquid crystal element and a storage capacitor which constitute a sub-pixel, and each form a pixel. In display control, the display-scan electrodes are driven sequentially, the thin-film transistors are turned ON for each display-scan electrode, and thus current is caused to flow between the source and drain of TFT concerned. The signal voltages supplied to the source electrode lines at this time are applied to the liquid crystal elements, whereby the transmissive state is controlled.
In order to reduce, in size, a structure that a liquid crystal panel and a touch panel are integrated into one unit, electrodes of the touch panel are arranged, in part, to double as the electrodes of the liquid crystal panel. If not so arranged, the electrodes of the touch panel and those of the liquid crystal panel are laid out close to each other. For instance, in a case where the display-scan electrodes of the liquid crystal panel double as the detection-scan electrodes of the touch panel or they are arranged close to the detection-scan electrodes, the coincidence between the liquid crystal panel and the touch panel in drive positions of their electrodes causes the interference between signals thereof, resulting in distorted display and the worsening of the accuracy of touch detection.
In such a case, on condition that the display frame cycle of the liquid crystal panel is equal to the detection frame cycle of the touch sensor, the coincidence of the timing of selecting the electrode between the liquid crystal panel and the touch panel can be avoided by setting a fixed phase difference between the cycle of driving the display-scan electrodes (i.e. the cycle of overwriting data on the liquid crystal elements) in the liquid crystal panel, and the drive cycle (i.e. touch-scan cycle) of the detection-scan electrodes in the touch panel. However, with the detection frame cycle of the touch sensor shorter than the display frame cycle of the liquid crystal panel, only setting the fixed phase difference is not adequate because there is always the timing with which the time of touch scan goes ahead of the time of overwriting the liquid crystal element, and the touch scan interferes with the display by the liquid crystal panel, posing a problem such as the distorted display.
For the problem like this, measures have been known.
Some of them are disclosed in JP-A-2011-13760. In the first measure taken therein, the electrodes are scanned while skipping at least one drive electrode (or two or more drive electrodes) at a point at which the drive of the electrode for detection scan would go ahead of the drive of the electrode for display scan or around it. This is so-called means for thinning touch detections. In the second measure, the scan for touch detection is performed dividedly so as to prevent the formation of a point at which the drive of the electrode for detection scan would go ahead of the drive of the electrode for display scan; the detection scan after the division will be performed on a total of m drive electrodes partially and sequentially.